Chlorine is one of the most frequently used disinfectants for water disinfection. Chlorine can be used for the deactivation of most microorganisms and it is relatively cheap.
Chlorine as a disinfectant
Chlorine is one of the most broadly used disinfectants. Chlorine is very relevant and powerful for the deactivation of pathogenic microorganisms. It can be easily applied, measures and controlled. It is really persistent and comparatively low cost.
Chlorine has been used for many applications, such as the deactivation of pathogens in drinking water, swimming pool water, and wastewater, for the disinfection of household areas and for textile bleaching.
How does chlorine disinfection work?
Chlorine destroys pathogens such as bacteria and viruses by breaking the chemical bonds in their molecules. Disinfectants are used for this reason consist of chlorine compounds which can exchange atoms with other compounds, such as enzymes in bacteria and other cells. While enzymes come in contact with chlorine, one or more of the hydrogen atoms in the molecule are changed by chlorine.so, it causes the entire molecule to change shape or fall apart. whereas enzymes do not function properly, a cell or bacterium will die.
underchloric acid and hypochlorite ions will form free chlorine when bound together. This results in disinfection. Both substances have very distinctive behaviour. underchloric acid is more sensitive and is a powerful disinfectant than hypochlorite. underchloric acid is separate into hydrochloric acid (HCl) and atomic oxygen (O). The oxygen atom is a powerful disinfectant.
The disinfecting properties of chlorine in water build on the oxidizing power of the free oxygen atoms and on chlorine substitution reactions.
By nature, the cell wall of pathogenic microorganisms is negatively charged. so, it can be penetrated by the neutral underchloric acid, rather than by the negatively charged hypochlorite ion. Underchloric acid can pierce slime layers, cell walls and protective layers of microorganisms and effectively kills pathogens as a result. The micro organisms will either die or suffer from reproductive failure.
The efficiency of disinfection is controlled by the pH of the water. disinfection on chlorine will take place best when the pH is between 5,5 and 7,5. under chloric acid (HOCl) reacts faster than hypochlorite ions (OCl-); it is 80-100% more effective. The quantity of underchloric acid will decrease when the pH value is higher.
With a pH value of 6, the level of underchloric acid is 80% when the concentration of hypochlorite ions is 20%.
while the pH value is 8, this is the other way around.
while the pH value is 7,5, concentrations of underchloric acid and hypochlorite ions are equally high.
Which factors determine the effectivity of chlorine disinfection?
Factors which decide chlorine disinfection effectivity:
The factors are Chlorine concentrations, contact time, temperature, pH, number and types of microorganisms, concentrations of organic matter in the water.
Disinfection time for some different types of pathogenic microorganisms with chlorinated water, containing a chlorine concentration of 1 mg/L (1 ppm) when pH = 7,5 and T = 25 °C
Disinfection time of fecal pollutants with chlorinated water
E. coli 0157 H7 bacterium < 1 minute
Hepatitis A virus about 16 minutes
Giardia parasite about 45 minutes
Cryptosporidium about 9600 minutes (6,7 days)
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